ZOO 4910 Lecture Notes - Lecture 16: Gnathostomata, Photopsin, Rhodopsin
2 May 2018
School
Department
Course
Professor
Lancelets -no eye
•
Sea squirts -ocellus (single light sensitive cell)
•
Hagfish -eye spots
•
Lampreys -camera-like eye
•
Jawed vertebrates -fully developed eye
•
Evolution of the eye in Vertebrates:
Cornea: transparent protective layer
•
Choroid: pigmented epithelium behind retina
that increases visual sensitivity of retinal
pigments
•
Iris: pigmented smooth muscle
•
Pupil: opening in iris for light transfer
•
Lens: focuses image on fovea
•
Ciliary body: muscles for changing lens
•
Anatomy of the Vertebrate Eye:
Light travels through pupil and hits epithelial
cells at back of eye
•
Cone and rod cells transmit signal to nerves
within the eye where they transmit information
to the CNS
•
Mechanism:
Radio -microwave -infrared -visible light -
UV - x-ray -gamma
•
Visible light: ~500 nm wavelengths (2.48 electron
volts)
Rhodopsin in rods
!
Photopsin in cones
!
Disks in the outer segment contain
photopigments
○
Photopigments are proteins that absorb
energy from photons
○
Conformational change stimulates action
potentials
○
Photoreceptors:
•
Code for a protein ~350aa
○
Form 7 alpha-helix TM cored
○
Bind cis-retinal in pocket
○
Photons cause conformation change to
trans-retinal
○
Different aa changes = stronger/weaker
binding
○
Opsin Genes:
•
Integrated into epithelium of the choroid
○
Reflects light back to retina, increasing
night vision sensitivity
○
Tapetum lucideum:
•
Ability to detect different wavelengths of
light
○
Photoreceptors (rods, cones) are
sensitive to specific wavelengths
○
Dogs are dichromatic (blue and
yellow cones; no red/green)
!
Most mammals are monochromatic
○
Some birds, reptiles, and fish have up to
5 distinct colour photoreceptors (UV
receptor as well)
○
Colour vision:
•
Vision and Light:
Native to Africa/Eurasia
○
Has trichromatic vision
○
Grey Cheeked Mangabey, Japanese Macaque,
Guinea Baboon, & Roloway Monkey
•
Native to Central & South America
○
Has dichromatic vision (colour blind)
○
White Headed Capuchin, Black Squirrel
Monkey, White Faced Saki, & Pied Tamarin
•
Colour vision evolved via gene duplication and
mutation following the continental split ~50
million years ago
•
@154.219Mb
○
Tandemly duplicated genes on the X
chromosome
○
@ 154.144Mb
○
Human OPN1 gene duplicates:
•
Ex. Determining which leaves
have black fungus
!
Disease detection
○
*evidence suggests that colour
vision is related to the ability to
select ripe food or young leaves
(consume leaves with higher
protein:toughness ratio)
!
Trichomats selected
orange food items
(60%) and green food
items (40%)
!
Dichromats selected
orange food items
(46%) and green food
items (54%)
!
Part 1
□
If selected food with
circle were given
reward
!
Trained animals with
both types of vision
(primates)
!
Trichromatic vision -
51% correct responses
!
Dichromatic vision -
85% correct responses
!
Trichromatic
vision is more
likely to be
selected for
when food is
distinguished
from non-food
by colour
◊
Dichromatic
vision is more
likely to be
selected for
when food is
distinguished
from non-food
by shape
◊
Therefore,
!
Part 2
□
Food Selection Experiment:
!
Selection ripe and/or palatable food
○
*Alternate Hypothesis: natural selection for
trichromatic vision
•
Evolution of Colour Vision:
Muscles more the entire lens with
respect to the retina to focus (accomdate
far vs. near target)
○
Lens of teleosts are spherical with a high
refractive index
•
Muscles change the shape of the
elliptical lens to focus
○
Terrestrical vertebrates have convex lens
•
Depending on water quality, fish can
tune eyes to the blue or red spectrum
○
Salmon swimming upstream to spawn, switch
from vitamin A1 to A2 (via Cyp27c1) to
increase long-wave (infrared) ability in murky
water
•
Vision and Light Under Water:
Fundamentals and diversity of vision among
vertebrates
•
Adaptations for seeing at night and in low light
•
Evolution and ecology of colour vision
•
Vision under water
•
Summary:
11/22/17
Blue light transmits the farthest (>20m)
○
Creates a different light environment
○
Get attenuation of light in marine environments
•
There is wide convergent evolution of
fluorescent communication
○
Biofluorescent colours vary from green-red-
brown/orange
•
Biofluorescence in Catsharks: fundamental
desciption and relevance for elasmobranch
visual ecology
•
Biofluorescence -getting creative with
communication in a limited light environment
Evolved independently in several families of
snakes (pythons, boas, pit vipers)
•
Pit organ detects body heat given off by
prey --> converges with visual system to create
a thermal image
•
Communicates with the brain via the
trigeminal (TG) nerve (=cranial nerve V)
○
The pit membrane within the cavity is
connected to TG fibres
•
Outer = shield to visual light
○
*see slide
!
Bypass filter so more radiation can enter
○
Pits have different specialized structures
•
Unlike light-triggered chemical receptors
(opsins) in eyes, use heat sensitive receptors
that activate trigeminal neurons
•
Nocireceptor (pain receptor) is identidied
in the detection of noxious chemical in
humans
○
Point mutation in certain repeats cause
heat/cold syndrome
○
Mechanism in snakes is unknown
○
A tetrameric cellular membrane pore molecule
homologous to transient receptor potential
ankyrin 1 (TRPA1) is most likely the candidate
for heat sensing receptor in snakes
•
Spontaneous discharge
○
Stimulation by a 830nm laser
○
Response to a cold object: dissipates
thermal radiation
○
Action potential recorded from infrared
neurons on the optic tectum:
•
Similar image formation to that
transduced by light activation in the eyes
of vertebrates
○
It is the brain that "sees" an image
○
Infrared information from the trigeminal
ganglion is processed in the optic tectum
•
Predator avoidance
○
Prey capture
○
Thermoregulation
○
Ecological implications for:
•
Also processed by trigeminal neurons
○
Infrared sensitive cells have a large
diameter
○
There is convergent evolution of pit organs in
vampire bats:
•
Infrared Sensory Systems
Search phase -approach phase -terminal buzz
phase
•
*Echolocation in bats is also seen in cetaceans, small
mammals, oilbirds & swiftlets
Vomeronasal organ
○
Jacobson's organ connects directly to the
brain
○
Tongue fits into the grooves
○
Provides directional information
○
In snakes:
•
Up to 20% of inhaled air is directed into
olfactory epithelium
○
Due to quantity and quality of
olfactory epithelium
!
Dog sense of smell is 10-100 thousand
times more acute than a human
○
Mammals have most well-developed
sense of smell
○
*see variety of receptors
○
In mammals:
•
Many pseudogenes in mammals
○
Humans have major loss of
odorant receptors
!
Major loss of V1R and V2R genes in
chicken, dog/cow and primates
○
Odorant receptors are one of the largest
gene families in vertebrates
○
The number of receptors varies across taxa
•
*see slide
○
From transition from water to land, OR
type 1 & V2R are at significantly higher
concentrations
○
Olfactory higher in land vs. water
(compared to vomeronasal receptors)
○
Evolution:
•
Specialized olfactory processeing center
in the brain
○
Density of receptors in epithelium and
neurons in the brain determine sensitivity
○
Specialized intake to direct flow and
increase function
○
Most epithelium is used for chemical diffusion
•
Chemosensory taste buds are responsible
for detecting 5 main tastes: sweet, sour,
bitter, salty, umami (glutamate)
○
Cell types may be varied and
specific for detecting different
taste classes
!
Taste buds may contain 1 or 2 taste-
specific bipolar cells or up to several
hundred cells
○
Epithelial sodium channel
!
Cation nuclear gated gustatory
!
Voltage gated
!
*see slide for others
!
Different classes of bipolar cells in taste
buds:
○
GPCR: umami, bitter, sweet (not
salty/sour)
!
Different chemosensory receptors were
discovered in vertebrates
○
Taste:
•
Use taste-bud receptors on skin
○
Catfish sensitivity in highest in natural
seawater (pH 8.2)
○
Climate change = ocean acidification
○
Cannot pick up differences in pH
below 8
!
Sea water pH dropping to 8.1 (estimated
to reach pH 8 before 2100)
○
pH sensing in Catfish:
•
Chemical Reception:
Use ampullae for electroreception
•
Frequency enters pore and reaches ampullae
which sends signal to the nervous system
•
Electroreception: chondrichthyes
Disrupted magnetic field around bats,
mice, sea turtles, and homing pigeons
○
--> severe disruption of orientation
behaviour
○
Experiment:
•
Animals use a magnetic compass
○
Hypothesized:
•
When activated by blue light,
unpaired electrons spin depending
on surrounding magnetic field
!
Cryptochrome: a photoreceptive protein
expressed in bird eyes, sensitive to blue
light
1.
Expressed in the beak of bird
species, trout snouts, eastern newt
bodies and is suspected in many
others
!
*see slide
!
Iron Oxide (Magnetite): an iron based
substance that can become magnetized
and align in linear arrangements
2.
Two primary hypotheses:
•
MagR gene: binds iron located in the
head, and forms a complex with
crptochrome
○
20 MagR molecules
!
10 cyrptochromes
!
Cylinder formation:
○
Magnetosensory protein cystals were
produced and observed in a rotating
magenetic field
○
MagR/Cry4 localize to distinct eye
layers in the pigeon
○
Why are both hypotheses are supported?
•
Magnetoreception:
Diversity among vertebrates
○
Disparity in specificity of various senses
○
Evolutionary substrates for sensory systems
•
Infrared perception
○
Chemoreception
○
Magnetoreception
○
Physiological mechanisms and ecological
implications of:
•
Summary:
Sensing the Environment
Friday,*November* 17,*2017
4:51*PM
Lancelets -no eye
•
Sea squirts -ocellus (single light sensitive cell)
•
Hagfish -eye spots
•
Lampreys -camera-like eye
•
Jawed vertebrates -fully developed eye
•
Evolution of the eye in Vertebrates:
Cornea: transparent protective layer
•
Choroid: pigmented epithelium behind retina
that increases visual sensitivity of retinal
pigments
•
Iris: pigmented smooth muscle
•
Pupil: opening in iris for light transfer
•
Lens: focuses image on fovea
•
Ciliary body: muscles for changing lens
•
Anatomy of the Vertebrate Eye:
Light travels through pupil and hits epithelial
cells at back of eye
•
Cone and rod cells transmit signal to nerves
within the eye where they transmit information
to the CNS
•
Mechanism:
Radio -microwave -infrared -visible light -
UV - x-ray -gamma
•
Visible light: ~500 nm wavelengths (2.48 electron
volts)
Rhodopsin in rods
!
Photopsin in cones
!
Disks in the outer segment contain
photopigments
○
Photopigments are proteins that absorb
energy from photons
○
Conformational change stimulates action
potentials
○
Photoreceptors:
•
Code for a protein ~350aa
○
Form 7 alpha-helix TM cored
○
Bind cis-retinal in pocket
○
Photons cause conformation change to
trans-retinal
○
Different aa changes = stronger/weaker
binding
○
Opsin Genes:
•
Integrated into epithelium of the choroid
○
Reflects light back to retina, increasing
night vision sensitivity
○
Tapetum lucideum:
•
Ability to detect different wavelengths of
light
○
Photoreceptors (rods, cones) are
sensitive to specific wavelengths
○
Dogs are dichromatic (blue and
yellow cones; no red/green)
!
Most mammals are monochromatic
○
Some birds, reptiles, and fish have up to
5 distinct colour photoreceptors (UV
receptor as well)
○
Colour vision:
•
Vision and Light:
Native to Africa/Eurasia
○
Has trichromatic vision
○
Grey Cheeked Mangabey, Japanese Macaque,
Guinea Baboon, & Roloway Monkey
•
Native to Central & South America
○
Has dichromatic vision (colour blind)
○
White Headed Capuchin, Black Squirrel
Monkey, White Faced Saki, & Pied Tamarin
•
Colour vision evolved via gene duplication and
mutation following the continental split ~50
million years ago
•
@154.219Mb
○
Tandemly duplicated genes on the X
chromosome
○
@ 154.144Mb
○
Human OPN1 gene duplicates:
•
Ex. Determining which leaves
have black fungus
!
Disease detection
○
*evidence suggests that colour
vision is related to the ability to
select ripe food or young leaves
(consume leaves with higher
protein:toughness ratio)
!
Trichomats selected
orange food items
(60%) and green food
items (40%)
!
Dichromats selected
orange food items
(46%) and green food
items (54%)
!
Part 1
□
If selected food with
circle were given
reward
!
Trained animals with
both types of vision
(primates)
!
Trichromatic vision -
51% correct responses
!
Dichromatic vision -
85% correct responses
!
Trichromatic
vision is more
likely to be
selected for
when food is
distinguished
from non-food
by colour
◊
Dichromatic
vision is more
likely to be
selected for
when food is
distinguished
from non-food
by shape
◊
Therefore,
!
Part 2
□
Food Selection Experiment:
!
Selection ripe and/or palatable food
○
*Alternate Hypothesis: natural selection for
trichromatic vision
•
Evolution of Colour Vision:
Muscles more the entire lens with
respect to the retina to focus (accomdate
far vs. near target)
○
Lens of teleosts are spherical with a high
refractive index
•
Muscles change the shape of the
elliptical lens to focus
○
Terrestrical vertebrates have convex lens
•
Depending on water quality, fish can
tune eyes to the blue or red spectrum
○
Salmon swimming upstream to spawn, switch
from vitamin A1 to A2 (via Cyp27c1) to
increase long-wave (infrared) ability in murky
water
•
Vision and Light Under Water:
Fundamentals and diversity of vision among
vertebrates
•
Adaptations for seeing at night and in low light
•
Evolution and ecology of colour vision
•
Vision under water
•
Summary:
11/22/17
Blue light transmits the farthest (>20m)
○
Creates a different light environment
○
Get attenuation of light in marine environments
•
There is wide convergent evolution of
fluorescent communication
○
Biofluorescent colours vary from green-red-
brown/orange
•
Biofluorescence in Catsharks: fundamental
desciption and relevance for elasmobranch
visual ecology
•
Biofluorescence -getting creative with
communication in a limited light environment
Evolved independently in several families of
snakes (pythons, boas, pit vipers)
•
Pit organ detects body heat given off by
prey --> converges with visual system to create
a thermal image
•
Communicates with the brain via the
trigeminal (TG) nerve (=cranial nerve V)
○
The pit membrane within the cavity is
connected to TG fibres
•
Outer = shield to visual light
○
*see slide
!
Bypass filter so more radiation can enter
○
Pits have different specialized structures
•
Unlike light-triggered chemical receptors
(opsins) in eyes, use heat sensitive receptors
that activate trigeminal neurons
•
Nocireceptor (pain receptor) is identidied
in the detection of noxious chemical in
humans
○
Point mutation in certain repeats cause
heat/cold syndrome
○
Mechanism in snakes is unknown
○
A tetrameric cellular membrane pore molecule
homologous to transient receptor potential
ankyrin 1 (TRPA1) is most likely the candidate
for heat sensing receptor in snakes
•
Spontaneous discharge
○
Stimulation by a 830nm laser
○
Response to a cold object: dissipates
thermal radiation
○
Action potential recorded from infrared
neurons on the optic tectum:
•
Similar image formation to that
transduced by light activation in the eyes
of vertebrates
○
It is the brain that "sees" an image
○
Infrared information from the trigeminal
ganglion is processed in the optic tectum
•
Predator avoidance
○
Prey capture
○
Thermoregulation
○
Ecological implications for:
•
Also processed by trigeminal neurons
○
Infrared sensitive cells have a large
diameter
○
There is convergent evolution of pit organs in
vampire bats:
•
Infrared Sensory Systems
Search phase -approach phase -terminal buzz
phase
•
*Echolocation in bats is also seen in cetaceans, small
mammals, oilbirds & swiftlets
Vomeronasal organ
○
Jacobson's organ connects directly to the
brain
○
Tongue fits into the grooves
○
Provides directional information
○
In snakes:
•
Up to 20% of inhaled air is directed into
olfactory epithelium
○
Due to quantity and quality of
olfactory epithelium
!
Dog sense of smell is 10-100 thousand
times more acute than a human
○
Mammals have most well-developed
sense of smell
○
*see variety of receptors
○
In mammals:
•
Many pseudogenes in mammals
○
Humans have major loss of
odorant receptors
!
Major loss of V1R and V2R genes in
chicken, dog/cow and primates
○
Odorant receptors are one of the largest
gene families in vertebrates
○
The number of receptors varies across taxa
•
*see slide
○
From transition from water to land, OR
type 1 & V2R are at significantly higher
concentrations
○
Olfactory higher in land vs. water
(compared to vomeronasal receptors)
○
Evolution:
•
Specialized olfactory processeing center
in the brain
○
Density of receptors in epithelium and
neurons in the brain determine sensitivity
○
Specialized intake to direct flow and
increase function
○
Most epithelium is used for chemical diffusion
•
Chemosensory taste buds are responsible
for detecting 5 main tastes: sweet, sour,
bitter, salty, umami (glutamate)
○
Cell types may be varied and
specific for detecting different
taste classes
!
Taste buds may contain 1 or 2 taste-
specific bipolar cells or up to several
hundred cells
○
Epithelial sodium channel
!
Cation nuclear gated gustatory
!
Voltage gated
!
*see slide for others
!
Different classes of bipolar cells in taste
buds:
○
GPCR: umami, bitter, sweet (not
salty/sour)
!
Different chemosensory receptors were
discovered in vertebrates
○
Taste:
•
Use taste-bud receptors on skin
○
Catfish sensitivity in highest in natural
seawater (pH 8.2)
○
Climate change = ocean acidification
○
Cannot pick up differences in pH
below 8
!
Sea water pH dropping to 8.1 (estimated
to reach pH 8 before 2100)
○
pH sensing in Catfish:
•
Chemical Reception:
Use ampullae for electroreception
•
Frequency enters pore and reaches ampullae
which sends signal to the nervous system
•
Electroreception: chondrichthyes
Disrupted magnetic field around bats,
mice, sea turtles, and homing pigeons
○
--> severe disruption of orientation
behaviour
○
Experiment:
•
Animals use a magnetic compass
○
Hypothesized:
•
When activated by blue light,
unpaired electrons spin depending
on surrounding magnetic field
!
Cryptochrome: a photoreceptive protein
expressed in bird eyes, sensitive to blue
light
1.
Expressed in the beak of bird
species, trout snouts, eastern newt
bodies and is suspected in many
others
!
*see slide
!
Iron Oxide (Magnetite): an iron based
substance that can become magnetized
and align in linear arrangements
2.
Two primary hypotheses:
•
MagR gene: binds iron located in the
head, and forms a complex with
crptochrome
○
20 MagR molecules
!
10 cyrptochromes
!
Cylinder formation:
○
Magnetosensory protein cystals were
produced and observed in a rotating
magenetic field
○
MagR/Cry4 localize to distinct eye
layers in the pigeon
○
Why are both hypotheses are supported?
•
Magnetoreception:
Diversity among vertebrates
○
Disparity in specificity of various senses
○
Evolutionary substrates for sensory systems
•
Infrared perception
○
Chemoreception
○
Magnetoreception
○
Physiological mechanisms and ecological
implications of:
•
Summary:
Sensing the Environment
Friday,*November* 17,*2017 4:51*PM
Lancelets -no eye
•
Sea squirts -ocellus (single light sensitive cell)
•
Hagfish -eye spots
•
Lampreys -camera-like eye
•
Jawed vertebrates -fully developed eye
•
Evolution of the eye in Vertebrates:
Cornea: transparent protective layer
•
Choroid: pigmented epithelium behind retina
that increases visual sensitivity of retinal
pigments
•
Iris: pigmented smooth muscle
•
Pupil: opening in iris for light transfer
•
Lens: focuses image on fovea
•
Ciliary body: muscles for changing lens
•
Anatomy of the Vertebrate Eye:
Light travels through pupil and hits epithelial
cells at back of eye
•
Cone and rod cells transmit signal to nerves
within the eye where they transmit information
to the CNS
•
Mechanism:
Radio -microwave -infrared -visible light -
UV - x-ray -gamma
•
Visible light: ~500 nm wavelengths (2.48 electron
volts)
Rhodopsin in rods
!
Photopsin in cones
!
Disks in the outer segment contain
photopigments
○
Photopigments are proteins that absorb
energy from photons
○
Conformational change stimulates action
potentials
○
Photoreceptors:
•
Code for a protein ~350aa
○
Form 7 alpha-helix TM cored
○
Bind cis-retinal in pocket
○
Photons cause conformation change to
trans-retinal
○
Different aa changes = stronger/weaker
binding
○
Opsin Genes:
•
Integrated into epithelium of the choroid
○
Reflects light back to retina, increasing
night vision sensitivity
○
Tapetum lucideum:
•
Ability to detect different wavelengths of
light
○
Photoreceptors (rods, cones) are
sensitive to specific wavelengths
○
Dogs are dichromatic (blue and
yellow cones; no red/green)
!
Most mammals are monochromatic
○
Some birds, reptiles, and fish have up to
5 distinct colour photoreceptors (UV
receptor as well)
○
Colour vision:
•
Vision and Light:
Native to Africa/Eurasia
○
Has trichromatic vision
○
Grey Cheeked Mangabey, Japanese Macaque,
Guinea Baboon, & Roloway Monkey
•
Native to Central & South America
○
Has dichromatic vision (colour blind)
○
White Headed Capuchin, Black Squirrel
Monkey, White Faced Saki, & Pied Tamarin
•
Colour vision evolved via gene duplication and
mutation following the continental split ~50
million years ago
•
@154.219Mb
○
Tandemly duplicated genes on the X
chromosome
○
@ 154.144Mb
○
Human OPN1 gene duplicates:
•
Ex. Determining which leaves
have black fungus
!
Disease detection
○
*evidence suggests that colour
vision is related to the ability to
select ripe food or young leaves
(consume leaves with higher
protein:toughness ratio)
!
Trichomats selected
orange food items
(60%) and green food
items (40%)
!
Dichromats selected
orange food items
(46%) and green food
items (54%)
!
Part 1
□
If selected food with
circle were given
reward
!
Trained animals with
both types of vision
(primates)
!
Trichromatic vision -
51% correct responses
!
Dichromatic vision -
85% correct responses
!
Trichromatic
vision is more
likely to be
selected for
when food is
distinguished
from non-food
by colour
◊
Dichromatic
vision is more
likely to be
selected for
when food is
distinguished
from non-food
by shape
◊
Therefore,
!
Part 2
□
Food Selection Experiment:
!
Selection ripe and/or palatable food
○
*Alternate Hypothesis: natural selection for
trichromatic vision
•
Evolution of Colour Vision:
Muscles more the entire lens with
respect to the retina to focus (accomdate
far vs. near target)
○
Lens of teleosts are spherical with a high
refractive index
•
Muscles change the shape of the
elliptical lens to focus
○
Terrestrical vertebrates have convex lens
•
Depending on water quality, fish can
tune eyes to the blue or red spectrum
○
Salmon swimming upstream to spawn, switch
from vitamin A1 to A2 (via Cyp27c1) to
increase long-wave (infrared) ability in murky
water
•
Vision and Light Under Water:
Fundamentals and diversity of vision among
vertebrates
•
Adaptations for seeing at night and in low light
•
Evolution and ecology of colour vision
•
Vision under water
•
Summary:
11/22/17
Blue light transmits the farthest (>20m)
○
Creates a different light environment
○
Get attenuation of light in marine environments
•
There is wide convergent evolution of
fluorescent communication
○
Biofluorescent colours vary from green-red-
brown/orange
•
Biofluorescence in Catsharks: fundamental
desciption and relevance for elasmobranch
visual ecology
•
Biofluorescence -getting creative with
communication in a limited light environment
Evolved independently in several families of
snakes (pythons, boas, pit vipers)
•
Pit organ detects body heat given off by
prey --> converges with visual system to create
a thermal image
•
Communicates with the brain via the
trigeminal (TG) nerve (=cranial nerve V)
○
The pit membrane within the cavity is
connected to TG fibres
•
Outer = shield to visual light
○
*see slide
!
Bypass filter so more radiation can enter
○
Pits have different specialized structures
•
Unlike light-triggered chemical receptors
(opsins) in eyes, use heat sensitive receptors
that activate trigeminal neurons
•
Nocireceptor (pain receptor) is identidied
in the detection of noxious chemical in
humans
○
Point mutation in certain repeats cause
heat/cold syndrome
○
Mechanism in snakes is unknown
○
A tetrameric cellular membrane pore molecule
homologous to transient receptor potential
ankyrin 1 (TRPA1) is most likely the candidate
for heat sensing receptor in snakes
•
Spontaneous discharge
○
Stimulation by a 830nm laser
○
Response to a cold object: dissipates
thermal radiation
○
Action potential recorded from infrared
neurons on the optic tectum:
•
Similar image formation to that
transduced by light activation in the eyes
of vertebrates
○
It is the brain that "sees" an image
○
Infrared information from the trigeminal
ganglion is processed in the optic tectum
•
Predator avoidance
○
Prey capture
○
Thermoregulation
○
Ecological implications for:
•
Also processed by trigeminal neurons
○
Infrared sensitive cells have a large
diameter
○
There is convergent evolution of pit organs in
vampire bats:
•
Infrared Sensory Systems
Search phase -approach phase -terminal buzz
phase
•
*Echolocation in bats is also seen in cetaceans, small
mammals, oilbirds & swiftlets
Vomeronasal organ
○
Jacobson's organ connects directly to the
brain
○
Tongue fits into the grooves
○
Provides directional information
○
In snakes:
•
Up to 20% of inhaled air is directed into
olfactory epithelium
○
Due to quantity and quality of
olfactory epithelium
!
Dog sense of smell is 10-100 thousand
times more acute than a human
○
Mammals have most well-developed
sense of smell
○
*see variety of receptors
○
In mammals:
•
Many pseudogenes in mammals
○
Humans have major loss of
odorant receptors
!
Major loss of V1R and V2R genes in
chicken, dog/cow and primates
○
Odorant receptors are one of the largest
gene families in vertebrates
○
The number of receptors varies across taxa
•
*see slide
○
From transition from water to land, OR
type 1 & V2R are at significantly higher
concentrations
○
Olfactory higher in land vs. water
(compared to vomeronasal receptors)
○
Evolution:
•
Specialized olfactory processeing center
in the brain
○
Density of receptors in epithelium and
neurons in the brain determine sensitivity
○
Specialized intake to direct flow and
increase function
○
Most epithelium is used for chemical diffusion
•
Chemosensory taste buds are responsible
for detecting 5 main tastes: sweet, sour,
bitter, salty, umami (glutamate)
○
Cell types may be varied and
specific for detecting different
taste classes
!
Taste buds may contain 1 or 2 taste-
specific bipolar cells or up to several
hundred cells
○
Epithelial sodium channel
!
Cation nuclear gated gustatory
!
Voltage gated
!
*see slide for others
!
Different classes of bipolar cells in taste
buds:
○
GPCR: umami, bitter, sweet (not
salty/sour)
!
Different chemosensory receptors were
discovered in vertebrates
○
Taste:
•
Use taste-bud receptors on skin
○
Catfish sensitivity in highest in natural
seawater (pH 8.2)
○
Climate change = ocean acidification
○
Cannot pick up differences in pH
below 8
!
Sea water pH dropping to 8.1 (estimated
to reach pH 8 before 2100)
○
pH sensing in Catfish:
•
Chemical Reception:
Use ampullae for electroreception
•
Frequency enters pore and reaches ampullae
which sends signal to the nervous system
•
Electroreception: chondrichthyes
Disrupted magnetic field around bats,
mice, sea turtles, and homing pigeons
○
--> severe disruption of orientation
behaviour
○
Experiment:
•
Animals use a magnetic compass
○
Hypothesized:
•
When activated by blue light,
unpaired electrons spin depending
on surrounding magnetic field
!
Cryptochrome: a photoreceptive protein
expressed in bird eyes, sensitive to blue
light
1.
Expressed in the beak of bird
species, trout snouts, eastern newt
bodies and is suspected in many
others
!
*see slide
!
Iron Oxide (Magnetite): an iron based
substance that can become magnetized
and align in linear arrangements
2.
Two primary hypotheses:
•
MagR gene: binds iron located in the
head, and forms a complex with
crptochrome
○
20 MagR molecules
!
10 cyrptochromes
!
Cylinder formation:
○
Magnetosensory protein cystals were
produced and observed in a rotating
magenetic field
○
MagR/Cry4 localize to distinct eye
layers in the pigeon
○
Why are both hypotheses are supported?
•
Magnetoreception:
Diversity among vertebrates
○
Disparity in specificity of various senses
○
Evolutionary substrates for sensory systems
•
Infrared perception
○
Chemoreception
○
Magnetoreception
○
Physiological mechanisms and ecological
implications of:
•
Summary:
Sensing the Environment
Friday,*November* 17,*2017 4:51*PM
Document Summary
Sea squirts - ocellus (single light sensitive cell) Choroid: pigmented epithelium behind retina that increases visual sensitivity of retinal pigments. Light travels through pupil and hits epithelial cells at back of eye. Cone and rod cells transmit signal to nerves within the eye where they transmit information to the cns. Visible light: ~500 nm wavelengths (2. 48 electron volts) Radio - microwave - infrared - visible light - Photopigments are proteins that absorb energy from photons. Reflects light back to retina, increasing night vision sensitivity. Photoreceptors (rods, cones) are sensitive to specific wavelengths. Dogs are dichromatic (blue and yellow cones; no red/green) Some birds, reptiles, and fish have up to. 5 distinct colour photoreceptors (uv receptor as well) Colour vision evolved via gene duplication and mutation following the continental split ~50 million years ago. *evidence suggests that colour vision is related to the ability to select ripe food or young leaves (consume leaves with higher protein:toughness ratio)
